i) Field of the Invention
The present invention relates to a lubricant for use in refrigerators and to a composition for use in refrigerators using said lubricant. More specifically, the present invention relates to a lubricant for use in refrigerators employing a chlorine-free Flon-type coolant such as Flon 134a (1,1,2,2,2-tetrafluoroethane), Flon 32 (difluoromethane), Flon 125 (1,1,2,2-pentafluoroethane), Flon 143a (1,1,1-trifluoroethane), Flon 152a (1,1-difluoroethane), Flon 134 (1,1,2,2-tetrafluoroethane), and the like, and a composition for use in refrigerators using said lubricant.
ii) Description of the Related Art
Flon-type coolants have conventionally been excellent for use as a coolant for refrigerators as they are chemically stable and have low toxicity. However, the recent Montreal Protocol decided that among these Flon-type coolants the use of chlorofluorocarbons such as Flon 12 (dichlorodifluoromethane) shall be totally abolished by the year 2000, because chlorofluorocarbons are a source of damage to the ozone layer in the stratosphere and contribute to global warming.
In such circumstances, Flon-type coolants not having chlorine in the molecules thereof, i.e. chlorine-free Flon-type coolants have been developed and are representatively illustrated by Flon 134a, described above, as an alternative to Flon 12.
However, because the polarity of chlorine-free Flon-type coolants without chlorine in molecules thereof such as Flon 134a and the like is higher than Flon 12, these chlorine-free Flon-type coolants have poor compatibility with naphthene mineral oils, alkylbenzene and the like which have been employed as lubricants for refrigerators and cause poor lubricity and frictional wear in the compressors of refrigerators. Therefore, a lubricant having good compatibility with Flon 134a and the like has been sought.
As a lubricant for refrigerators using Flon 134a as a coolant, polyoxyalkylene glycol has been disclosed in U.S. Pat. No. 4,755,316, Japanese Patent Laid-Open Nos. 01-271491, 02-129294, 03-103496 and the like, polyoxyalkylene glycol containing an acyl group as a modified compound of polyoxyalkylene glycol has been disclosed in Japanese Patent Laid-Open Nos. 01-198694, 03-33193, 03-79696, 03-81396 and the like, and polyoxyalkylene glycol containing halogen group has been disclosed in Japanese Patent Laid-Open Nos. 02-180987 and 02-132176.
However, since the above polyoxyalkylene glycols are highly hygroscopic and have poor stability, those modified compounds of polyoxyalkylene glycol have problems with corrosiveness and also, dialkylethers of polyoxyalkylene glycol have poor lubricity, so all of these lubricants have not been practical.
On the other hand, Japanese Patent Laid-Open Nos. 01-259093, 01-259095, 02-43290, 02-84491, 02-102296, 02-182780, 02-242888, 02-277097, 02-281098, 03-50297, 03-103496, 03-103497, 03-50297 and the like disclose monoalkylethers of polyoxyalkylene glycols that have good stability and no corrosive properties and are expected to be practicable.
However, the publicly known monoalkylethers of polyoxyalkylene glycol, described above, still have insufficient lubricity and further have poor compatibility with chlorine-free Flon-type coolants such as Flon 134a and the like.
Accordingly, it is an object of the present invention to provide a lubricant for use in refrigerators having superior compatibility with chlorine-free Flon-type coolants, good lubricity and resistance to hygroscopicity and also a composition for refrigerators using said lubricant.